Hey, Rob;
just out of curiosity, I checked out MOHAWK's waterbourne sanding sealer. Here's the contents...scroll down a bit for the ingredients.
Seems like it's basically acrylic resin, not polyurethane.http://www.mohawk-finishing.com/mhk_...MA640-1067.pdf
How about just using an acrylic sealer?

Rob,over the years have found that you can use finish such as lac. And poly. For sealers.only problem they dont have sanding agent in them,will seal wood ok, but wont sand as easy . Never had good luck with water base finish, always raised grain of wood more than i liked it to.later bowdean---are we having fun yet?

When you mix shellac for sanding sealer, it's very much thinned down with denatured alcohol. <-- Not at it's usual mix. The goal is for it to soak into the wood and be sucked up by it, and it dries below the surface... Until it just before it won't soak in the the surface any more. That takes some practice at that to get that right.

When you have done that (below the surface) then it will take stain evenly. If a paint out, then you don't worry that it will no longer soak anything into it... and can go hog-wild. With it thinned down so much, it is easy to sand away any excess and really doesn't load up on sand paper.

(IMHO)
If you already buy shellac flake and already have it on-hand... Mixing it thin is cheaper and one less trip to the stores to buy just sanding sealer. What I've noticed about store-bought sanding sealer, is that most seem to be a sort of cellulose affair, that fills the open pores to make it smooth at the surface... and when sanded, it doesn't seem to take stain in itself like I want it too. For paint-outs, I've used thinned down wood-filler or thinned down wood glue to do the same. If you are just doing a paint-out, any primer will work.

"Don't worry, I saw this work in a cartoon once.""Usually learning skills and tooling involves a progression of logical steps."